The present invention relates to a multi-layer printed circuit, in particular, relates to a double layer printed circuit for use in a thermal printer head.
With the advent of computer technology and advances in the arts of data processing and/or data communication, facsimile communication, requirements for increased speed of information handling have become more stringent. One known type of rapid printing is a high speed thermal printer, which has at least a thermal head and a printing paper, and operates on the principle that a thermal head, heated to a high temperature according to the pattern of a desired character to be printed, selectively changes the color of a thermal paper or causes the thermal ink to be printed on paper. A thermal printer has the advantage that it can print not only a predetermined pattern of characters but also any pattern desired including pictures, Chinese characters and/or Arabian characters.
A thermal printer is a kind of a dot printer which composes the pattern to be printed with a plurality of dots, and a thermal head has a plurality of heat cells arranged, for instance, in a straight line of heat cells; said heat cells are selectively heated, thus the thermal paper reacts chemically, and the color of the thermal paper is selectively changed. Thus, the desired pattern is printed on said paper.
Because of the principle of dot printing, the density of dots in a thermal head must be very high to provide a clear print, that is, the length between each heaters in a thermal head must be very short. Since the thermal heads are provided on a printed circuit, the structure of the printed circuit might restrict the density of the heaters, thereby restricting the quality of the printed pattern. A prior printed circuit for a thermal head has a complicated printed pattern structure, and the density of such thermal heads can not be high. Another disadvantage of a prior printed circuit for a thermal head is that the size of the printed circuit is large compared with the available length of the thermal heads. Still another disadvantage of a prior printed circuit is that some conductors connected to the heaters sometimes short-circuit with other circuits due to the high density of the circuit.